I own Sam Collins his ' Simple Repertoire for White' and downloaded/bought the pgn files from his ' killer c3 Sicilian' DVD but I can't find this 6.g6 move mentioned.

I face it regularly at my level. Did I overlook something? The move doesn't seem so bad it doesn't deserve to be mentioned.

This move does indeed deserve attention, if only because Black has scored well from over 250 games!

But I think it's a bit suspect and White should be able to gain an edge; possibly not with the stereotyped 7 Bc4 Nb6 8 Bb3 Bg7 though - this scores badly for White - but maybe with 7 Qb3, which seems to force Black to weaken his position with 7...e6 (7...Nb6 allows 8 d5!), after which 8 Nc3 might be enough for a small but long-term advantage.

7 Qb3 has been the choice of some strong players; it scores 60% from the 35 games I found. It's also the top line for the Stockfish 12 engine.

For further research it might be useful to compare with a) 6 Bc4 Nb6 7 Bb3 g6!? (8 cxd4 would transpose to the line with 7 Bc4 mentioned above) which has also been played by some strong players but in this particular move order Dave Smerdon endorsed 8 Ng5! (Esserman-Djukic, Cappelle 2016);b) the similar line in the English: 1 c4 e5 2 Nc3 Nf6 3 g3 c6 4 Nf3 e4 5 Nd4 Qb6 or 5...d5 6 cxd5 Qb6; in the Alapin line obviously White is a tempo up, which is likely to be important in such a semi-open position.